1. Field of the Invention
The invention concerns a light source module for motor vehicle headlamps as well as headlamps for such a light source module.
2. Description of the Related Art
Light-emitting diodes (LEDs) are being increasingly used as illuminants for vehicle headlamps. The advantages of the LED in comparison to conventional illuminants lies with the higher efficiency and a comparatively long service life. LEDs can also be constructed as compact modules. However, LEDs can often only achieve fairly low lighting intensities as compared to, for example, halogen lamps.
Laser light sources, particularly semiconductor lasers, offer a number of potentially advantageous properties, such as for example a comparatively small light-emitting area, high radiation intensities and luminance as well as the emission of largely collimated and polarized light beams. Optical systems for laser light can therefore be implemented in small spaces, for example as smaller focal lengths can be chosen than for optical systems for less strongly collimated light beams of for example light bulbs or conventional LEDs. The use of laser light sources can therefore allow for a compact construction of motor vehicle headlamps.
Generally speaking, one can distinguish between two types of light distributions for motor vehicle headlamps: the dimmed (low beam) distribution as well as the high beam distribution.
The low beam distribution is primarily intended to illuminate the area in front of the vehicle. This is supposed to prevent other road users, particularly opposing traffic, from being adversely affected (blinded). A low beam distribution (such as low beam headlamps, fog lights) therefore often have a light-dark threshold divided into horizontal sections. This division can also exhibit an adjusted contour, for example the light-dark threshold facing the opposing traffic can be vertically lower than the section facing away from the opposing traffic. Particularly, a diagonally ascending section of the light-dark threshold can be provided between these two horizontal sections (a so-called “Z-shape”).
The high beam distribution can be composed of a comparatively narrow lighting area (spot light distribution) above the light-dark threshold of the low beam distribution and a basic light distribution for the even illumination beneath or in the area of the light-dark threshold of the low beam light distribution.
In order to prevent adverse effects on other road users, the low beam light distribution is generally of lower intensity than the high beam one. High intensities are generally desired for the high beam distribution in order to illuminate areas that are further away. This is why the use of laser light sources is particularly beneficial for a high beam application.
Problems regarding the use of laser light sources for motor vehicle headlamps however arise, on one hand, from the fact that lasers generally emit a coherent, monochromatic light or light of a narrow wave length area. White mixed light is, however, usually desired or legally prescribed for the light emitted from motor vehicle headlamps. Furthermore, the emission distributions are supposed to exhibit certain, partially legally prescribed intensity curves (for example as described above). Measures for the conversion into suitable light must therefore be taken.
To convert monochromatic light into, for example, white mixed light, the use of photo luminescence converts or photo luminescence elements is generally known in the area of white LEDs or luminescence conversion LEDs. These consist, for example, of a photo luminescence coloring agent in a, for example, semi-transparent substrate and are arranged immediately on the light-emitting section of the LED. The light of a colored (for example blue) LED excites the photo luminescence coloring agent to start the photo luminescence process, which causes the photo luminescence coloring agent itself to emit light of a different wavelength (for example yellow). In this manner, at least a part of the emitted light of a wavelength range can be converted into light of a different wavelength range. Usually, another part of the emitted light is scattered by the photo luminescence element. The scattered light and the light emitted by the photo luminescence can then additively superimpose and achieve the desired, for example white, mixed light.
When using laser light sources, a precise adjustment of the laser light source to the photo luminescence element and possibly required optical devices for guiding, shaping or deflection of the laser light is needed due to the typically heavily collimated light beams with small beam diameters.
Known motor vehicle headlamps with laser light sources are therefore often fixedly installed inside the housing of the headlamp to prevent a misalignment of the laser light source in reference to the optical devices and/or the photo luminescence element. US 2012/0106178 A1, for example, describes an illumination device with a laser light source that is permanently arranged inside a housing reflector unit. Such arrangements complicate headlamp repairs if the laser light source fails. Manufacturing of a functional headlamp unit can also be complicated as well as complex as the laser light source has to be aligned inside the entire headlamp unit.